This invention relates generally to hydraulic devices, and particularly to hydraulic motors which include a gerotor gearset.
Hydraulic motors which include a gerotor gearset are well known. The gearset normally includes an outer internally-toothed member and an inner externally-toothed member. The teeth of the inner and outer toothed members define expansible and contractable fluid pockets therebetween. A commutating valve arrangement is utilized to direct fluid into the fluid pockets to effect expansion of the pockets and to direct fluid from the contracting pockets. The expansion and contraction of the fluid pockets results in relative rotary and orbital movement of the stator and rotor. The rotational movement is relatively slow as opposed to the orbiting movement and in a specific arrangement where an inner element has six teeth and an outer element has seven teeth, six orbits will occur for a single revolution.
Typically, the inner member (rotor) both orbits and rotates while the outer member (stator) is stationary. The teeth of the stator support and guide the rotor in its orbital and rotational movement. The rotor commonly orbits six times for each revolution and it is connected to an output shaft in a 1:1 relationship with rotation of the rotor. Such hydraulic motors are well known and are commonly referred to as low-speed high-torque motors. A typical example of such is shown in U.S. Pat. No. 3,289,602, and that disclosure is incorporated herein by reference.
One of the particular problems with the aforementioned known hydraulic motors centers around the output drive from the gearset. Commonly, a spline connection is provided between the output shaft and the rotor. The diameter of this drive shaft and spline connection is limited, of course, by the particular size of the rotor, and in the event that higher pressures or torques are desired to be produced by a gearset of a given size, breakage or damage to the drive shaft or spline can, and has occurred. To increase the diameter of the shaft without increasing the gearset size would entail increasing the size of the rotor bore in which the shaft is received, which would greatly weaken the rotor, and thereby increase the possibilities of rotor breakage.
Accordingly, the output drive from the rotor in hydraulic motors of the type to which the present invention is directed is a weak link in the torque-transmitting system. In order to obtain higher torques from such hydraulic motors, the diameters of the output shaft, as well as the diameter of the gerotor gearset, could be increased and, of course, such would increase the size of the housing for the motor and thus result in an overall larger motor size.